1. Field of the Invention
This invention relates to emissions control in a nonrecovery coking operation and more particularly to an improved nonrecovery coke oven door having means for capturing and incinerating gaseous and particulate combustion products at the base of the oven door.
2. Description of the Prior Art
The production of metallurgical coke by the nonrecovery process--once all but abandoned in favor of the by product or recovery process--has made a remarkable resurgence with the development of the Jewell-Thompson (Thompson) nonrecovery coke oven. A Thompson oven is disclosed and described in U.S. Pat. No. 5,114,542, reference to which may be had for a more complete understanding of the construction and operation of this type of coke oven. Since such nonrecovery ovens operate at sub-atmospheric (vacuum) pressure, many of the emissions control problems which plague by-product ovens are avoided. For example, the positive pressure within a by-product coke oven presents serious air pollution problems as a result of leakage around oven doors and charging hole covers in the oven roof throughout the coking cycle.
Thompson ovens are charged through an open door by a conveyor which is progressively projected into the oven from a charging and pushing car movable along rails at the pusher side of the battery. At the beginning of the charging operation, the door at the coke side of the oven is closed and a false door having a height equal to the desired depth of coal in the charge is positioned in the lower section of the pusher side door opening. The pusher side door is positioned against the end of the oven immediately above the conveyor to effectively close the door opening and thereby minimize air flow into the oven and the escape of pollutants from the oven during charging. When the oven is fully charged, the conveyor is retracted and the false door is removed to enable the oven door to be lowered and moved into position to close and seal the oven. This charging process and the apparatus used are described, for example, in U.S. Pat. No. 4,287,024.
As is known, coal to be coked in a Thompson oven is finely ground, or crushed, and is to some extent compacted by the weight of the drag type cantilevered charging conveyor so that the oven charge forms a relatively stable mass, or cake, in the hot oven. As the charging conveyor approaches the end of its travel through the oven, the ground coal flows into contact with and is compacted against the closed door on the coke side of the oven.
The hot refractory structure of the oven floor and walls ignites the coal on contact during charging, and some coal burning occurs. Since the oven is effectively closed during charging by the false door, the conveyor and the pusher side door, draft from the stack effectively prevents escape of emissions from this limited burning, and immediately upon closing the oven, a vacuum is applied throughout the oven chamber above the coal charge. While this vacuum is effective in withdrawing distillation products and emissions from the chamber above the coal charge and with the oven floor system as described in the above-mentioned U.S. Pat. No. 5,114,542, the depth of the charge and the dense or compact nature of the charge initially offers resistance to the upward flow of smoke and emissions from burning coal at the floor of the oven. As a result, a slight positive pressure can develop at or adjacent to the oven floor at the start of a coking cycle. This positive pressure can result in emissions from the bottom of the charge in the area adjacent to the oven doors escaping beneath the door, particularly the coke side door where the coal is more firmly packed against the door. As oxygen depletion from the air in the coal charge effectively slows and stops burning at the bottom of the charge, and gas escape channels are formed through the charge to the vacuum in the crown of the oven, the positive pressure is eliminated and the escape of emissions beneath the door ceases.
In order to limit the escape of emissions from beneath the bottom of the oven doors at the start of a coking cycle, it has been the practice to manually place a strip of a ceramic fiber insulating blanket in position overlapping the base of the door and the threshold when the doors are installed. This relatively dense blanket partially blocks any opening at the bottom of the door and filters particulates from any escaping combustion products. This practice has not been entirely satisfactory however not only because the blanket is incapable of completely blocking the escape of emissions, but also because it has to be manually placed against each door at the beginning of each cycle and manually removed prior to opening the door for pushing the oven. Further, the ceramic fiber blanket material is relatively expensive and is subject to damage so that it has to be replaced frequently. It is, therefore, an object of the present invention to provide an improved nonrecovery coke oven door which substantially eliminates the escape of pollutants from the vicinity of the oven door base.
The improved coke oven door of this invention includes means for applying a draft along the full width of the door at its base to draw pollutants from this area into a sealed passageway or duct system within the door frame or support structure and leading to the air inlet of the oven above the coal charge in that oven. Adjustable damper means preferably is provided in the duct system to control the draft applied at the base of the door. The door frame duct system is connected to the air inlet downstream of the process air regulating valves whereby the vacuum in the oven chamber can be regulated to draw a portion of the process air into the chamber through the duct system in the door to thereby substantially eliminate all emissions generated in the vicinity of the base of the door. The process air dampers may be closed, or partially closed, at the beginning of a coking cycle to assure an adequate draft applied along the base of the door. Shortly after the start of a cycle when the escape of emissions is no longer a problem, the process air dampers may be opened and the door duct system damper means closed for the remainder of the coking cycle.